Environmentally hazardous fluids such as acids, oils, and toxins which can cause serious harm to the environment often need to be pumped through fluid flow systems from one location to another. When pumping such dangerous flow materials, it is important that neither the liquid nor the gases which are often released by the liquid escape to the atmosphere or pump areas outside the desired fluid pumping path.
Heretofore, conventional mechanical seals have been developed in order to overcome rotating pump shaft sealing problems. These prior art mechanical seals allow for a fairly secure seal against the pumped fluids so as to prevent them from leaking or escaping axially along the shaft of the pump. Yet, in some cases the hazardous fluid being pumped penetrates these seals when the pressure within the pump becomes too high for the seal to handle, thus allowing the fluid to escape into the surrounding environment and/or the motor area of the pump.
Another problem with the aforesaid conventional mechanical seals is that gases (i.e. vapors) produced by the liquids being pumped and sealed against often escape. Conventional mechanical seals are often permeated by these vapors. One solution to this problem was the creation of an arrangement known in the art as a double seal with barrier fluid protection. In this type of arrangement, two seals form a cavity which is filled with a clean or environmentally safe barrier fluid. The seal facing the excess hazardous liquid (i.e. the first seal), that which does not exit the pump where desired, inhibits movement of the liquid sufficiently to prevent penetration of the seal by the liquid. The vapor produced by the liquid which permeates the first seal is stopped by the barrier fluid disposed in the cavity.
A drawback associated with these conventional double seal systems is that any failure by the first seal can defeat the entire double seal arrangement. If the first of the two seals breaks down, the barrier fluid is permitted to escape from the cavity in effect allowing the harmful gases to penetrate the second seal thus reaching the surrounding environment. Furthermore, the harmful liquid, after the break-down of the first seal, often penetrates the second seal thus creating both gaseous and liquid leakage. These leakages typically ruin the motor which drives the pump and pollute the surrounding environment.
The breaking of the aforesaid double seals is a problem of longstanding concern due to the fact that the barrier fluid in the cavity must be maintained at a relatively high barrier pressure in order to be effective. These high pressures within the cavity often result in a break or leak in one of the two seals.
U.S. Pat. No. 5,261,676, the disclosure of which is hereby incorporated herein by reference, discloses an environmentally safe pump including a rotating triplex seal construction disposed axially along the pump shaft. This patent is prior art to the instant application due to an offer for sale more than one year before the filing date of this application.
While the aforesaid triplex seal construction provides excellent results, it is felt that its three rotating annular sealing interfaces could be improved regarding their sensitivity to both temperature and pressure. The sealing interfaces between the rotating flange seals and stationary engaging members are preferably held to flatness tolerances of about two helium light bands (0.000023 inches) or less. Therefore, as in virtually all mechanical seals, small changes in temperature or pressure can minimize the effectiveness of the flatness of the sealing interface between the rotating sealing surfaces and their corresponding triplex stationary sealing members. For example, changes in temperature may cause the sealing surfaces to expand or contract thereby eventually creating a small gap through which the fluid to be sealed against can leak.
It is known to circulate cooling fluid to and from a pump chamber for the purpose of cooling or substantially maintaining the temperature of seals within the pump. However, such systems generally require an additional pump to circulate the cooling fluid, and the remotely positioned barrier or coolant tank is typically cooled by way of a blower separate and distinct from the blower/fan used to cool the pump motor. Thus, a pair of pumps and a pair of blowers are generally required in these types of systems, thereby increasing their cost and maintenance requirements.
It is apparent from the above that there exists a need in the art for a pump system including a seal construction which is even less sensitive to surrounding changes in temperature and pressure. Such a system must be simple, economical, and environmentally safe.
It is a purpose of this invention to fulfill the above-described needs, as well as other needs apparent to the skilled artisan from the following detailed description of this invention.